In human anatomy, the spine is a generally flexible column that can withstand tensile and compressive loads. The spine also allows bending motion and provides a place of attachment for keels, muscles, and ligaments. Generally, the spine is divided into four sections: the cervical spine, the thoracic or dorsal spine, the lumbar spine, and the pelvic spine. The pelvic spine generally includes the sacrum and the coccyx. The sections of the spine are made up of individual bones called vertebrae. Three joints reside between each set of two vertebrae: a larger intervertebral disc between the two vertebral bodies and two zygapophyseal joints located posterolaterally relative to the vertebral bodies and between opposing articular processes.
The intervertebral discs generally function as shock absorbers and as joints. Further, the intervertebral discs can absorb the compressive and tensile loads to which the spinal column can be subjected. At the same time, the intervertebral discs can allow adjacent vertebral bodies to move relative to each other, particularly during bending or flexure of the spine. Thus, the intervertebral discs are under constant muscular and gravitational pressure and generally, the intervertebral discs are the first parts of the lumbar spine to show signs of deterioration.
The zygapophyseal joints permit movement in the vertical direction, while limiting rotational motion of the two adjoining vertebrae. In addition, capsular ligaments surround the zygapophyseal joints, discouraging excess extension and torsion. In addition to intervertebral disc degradation, zygapophyseal joint degeneration is also common because the zygapophyseal joints are in almost constant motion with the spine. In fact, zygapophyseal joint degeneration and disc degeneration frequently occur together. Generally, although one can be the primary problem while the other is a secondary problem resulting from the altered mechanics of the spine, by the time surgical options are considered, both zygapophyseal joint degeneration and disc degeneration typically have occurred. For example, the altered mechanics of the zygapophyseal joints or the intervertebral disc can cause spinal stenosis, degenerative spondylolisthesis, and degenerative scoliosis.
Furthermore, acute strenuous events, such as whiplash or overextension, can damage capsular ligaments. Such damage to capsular ligaments if untreated can lead to degradation of the zygapophyseal joint or of the intervertebral disc.
In particular, deterioration can be manifested as a herniated disc. Weakness in an annulus fibrosis can result in a bulging of the nucleus pulposus or a herniation of the nucleus pulposus through the annulus fibrosis. Ultimately, weakness of the annulus fibrosis can result in a tear, permitting the nucleus pulposus to leak from the intervertebral space. Loss of the nucleus pulposus or a bulging of the nucleus pulposus can lead to pinching of nerves, causing pain and damage to vertebrae. In addition, aging can lead to a reduction in the hydration of the nucleus pulposus. Such a loss in hydration can also result in pinching of nerves.
A traditional option for treating a patient includes replacement of the intervertebral disc or the zygapophyseal joint with an implant. Another traditional option includes fusing adjacent vertebra using fasteners such as traditional screws or rods. However, such traditional methods are typically implemented with invasive surgical procedures. In particular, some traditional surgical procedures access the spine through the abdominal cavity, introducing risk to major organs and often leaving large scars.